From 1b7061d5bd43bbc33fc4d392384de5bf65d679c1 Mon Sep 17 00:00:00 2001
From: Sergio Estevao <sergioestevao@gmail.com>
Date: Fri, 18 May 2018 12:05:50 +0100
Subject: [PATCH] Add scrolling events.

---
 ios/RNRecyclerListView.swift    | 22 ++++++++++++++++++++++
 ios/RNRecyclerListViewManager.m |  2 ++
 src/RecyclerViewList.ios.js     | 14 ++++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/ios/RNRecyclerListView.swift b/ios/RNRecyclerListView.swift
index c3a6e2f85d740..c6a3f1fbead23 100644
--- a/ios/RNRecyclerListView.swift
+++ b/ios/RNRecyclerListView.swift
@@ -3,6 +3,10 @@ import UIKit
 
 @objc class RecyclerListView: UIView {
 
+    public var onVisibleItemsChange: RCTBubblingEventBlock?
+    public var firstVisibleIndex = -1
+    public var lastVisibleIndex = -1
+
     fileprivate var data = [RecyclerListItemView]()
 
     let cellIdentifier = "RecycleCell"
@@ -23,6 +27,7 @@ import UIKit
     
     func commonInit() {
         tableView.dataSource = self
+        tableView.delegate = self
         tableView.register(WrapperCell.self, forCellReuseIdentifier: cellIdentifier)
         tableView.rowHeight = UITableViewAutomaticDimension
         tableView.estimatedRowHeight = 80
@@ -81,6 +86,23 @@ extension RecyclerListView: UITableViewDataSource {
     }
 }
 
+extension RecyclerListView: UITableViewDelegate {
+
+    func scrollViewDidScroll(_ scrollView: UIScrollView) {
+
+        guard let visibleRows = tableView.indexPathsForVisibleRows,
+            let firstIndex = visibleRows.first?.row,
+            let lastIndex = visibleRows.last?.row else {
+            return
+        }
+        if firstVisibleIndex != firstIndex || lastVisibleIndex != lastIndex {
+            firstVisibleIndex = firstIndex
+            lastVisibleIndex = lastIndex
+            onVisibleItemsChange?(["firstIndex": firstIndex, "lastIndex": lastIndex])
+        }
+    }
+}
+
 extension RecyclerListView {
 
     @objc var dataSize: Int {
diff --git a/ios/RNRecyclerListViewManager.m b/ios/RNRecyclerListViewManager.m
index e452546ebaa71..662b972bc7990 100644
--- a/ios/RNRecyclerListViewManager.m
+++ b/ios/RNRecyclerListViewManager.m
@@ -79,6 +79,8 @@ - (void)executeBlock:(ListViewBlock)block onNode:(NSNumber *)node {
     view.dataSize = [RCTConvert NSInteger:json];
 }
 
+RCT_EXPORT_VIEW_PROPERTY(onVisibleItemsChange, RCTBubblingEventBlock)
+
 RCT_EXPORT_MODULE()
 
 @end
diff --git a/src/RecyclerViewList.ios.js b/src/RecyclerViewList.ios.js
index a156c3d83d973..ff63c191ba5a2 100644
--- a/src/RecyclerViewList.ios.js
+++ b/src/RecyclerViewList.ios.js
@@ -289,6 +289,20 @@ class RecyclerViewList extends React.PureComponent {
     return this._shouldUpdateAll || this._shouldUpdateKeys.includes(itemKey);
   }
 
+  _handleVisibleItemsChange = ({nativeEvent}) => {
+    var firstIndex = nativeEvent.firstIndex;
+    var lastIndex = nativeEvent.lastIndex;    
+    this.setState({
+                  firstVisibleIndex: firstIndex,
+                  lastVisibleIndex: lastIndex,
+                  });
+
+    const { onVisibleItemsChange } = this.props;
+    if (onVisibleItemsChange) {
+      onVisibleItemsChange(nativeEvent);
+    }
+  }
+
   _notifyItemMoved(currentPosition, nextPosition) {
     UIManager.dispatchViewManagerCommand(
                                          ReactNative.findNodeHandle(this),